The oxidation of polyoxyalkylene alcohols and glycols to their corresponding carboxylates in the presence of a free radical nitroxide and an NO.sub.x generating compound is described in various patents to Shell Oil Company by Herbert Fried. For example, U.S. Pat. No. 5,256,819 describes the oxidation of polyoxyalkylene glycols to their carboxylates in high yields (greater than about 98%) and high selectivities by using a free radical nitroxide, an NO.sub.x generating source, and an additional source of oxygen such as oxygen gas, in the presence of a solvent such as dichloromethane, triglyme, monoglyme, diglyme, tertiary amyl alcohol, acetonitrile, and the like. The results from the examples demonstrate degrees of conversion to the carboxylate in excess of 99%, with selectivities in excess of 99%.